1. Field of the Invention
This invention relates to a cutting tool for cutting a series of depressions along surfaces of roadways, and more particularly to a cutting tool which can automatically align itself with the surface being cut, thereby allowing it to continue to cut as it is moved forward.
2. Brief Description of the Prior Art
There has always been a concern that when a person is driving a vehicle it is often easy to drift off the road or over the center line and into the opposite lane of traffic, either of which can potentially lead to disastrous results. Therefore, a series of depressions are often cut along the shoulders or center line of the roadway and are referred to as ground in rumble strips. The purpose of the rumble strips is to alert drivers when they have drifted outside their traffic lane by creating a sound and causing vibration of the vehicle as the vehicle tires travel over the depressions.
A number of types of road surface grinders/cutting machines have heretofore been devised which use a cutting head or heads to cut individual depressions. The cutting heads are most often attached to or are part of a multipurpose power unit such as a tractor or skidsteer loader. The tractor or skidsteer loader is used to move the cutting head along the surface of the road and to provide any necessary utilities thereto, such as electricity or hydraulic fluid. The cutting head is then lowered into contact with the road surface to cut the depression.
Prior art cutting machines use a variety of methods for engaging and disengaging the cutting head into the road surface to cut the depression and for repositioning the cutting head for the next cut. One method of raising and lowering the cutting head requires an operator to manually control a hydraulic cylinder which is connected to the cutting head. A problem with this method is that it is difficult for the operator to move the cylinder controls quick enough to achieve a sufficient production rate.
An example of such a manually operated system is disclosed in U.S. Pat. No. 5,094,565 which utilizes a plurality of manually controlled cutting heads to cut a series of depressions at one time. The production rate is increased due to the use of the plurality of cutting heads, which are lowered onto the road surface to cut the depressions while the power unit is stationary. After the cut is complete, the cutting heads are raised and the power unit moves to the next location. Since there is not a continuous forward movement of the power unit, additional time is required for raising and lowering the cutting heads. Additionally, since the required sizing (depth, width, length, and radius of curvature of each depression) is specified depending on the task at hand, appropriately sized cutting heads must be used in order to meet the required dimensional sizing of the depressions. Thus, if different depression sizes are required, the cutting heads may have to be replaced.
In order to overcome some of the problems with the manual systems, automated means for raising and lowering the cutting head have been developed. Such means include rigidly connecting the cutting heads (1) to an eccentric wheel which rolls over the road surface or (2) to a cam and lever system. In each of these automated systems, the cutting head is automatically raised and lowered as the power unit moves forward due, respectively, to the rotation of the eccentric wheel and the action of the cam and levers. These systems are an improvement over the manually operated systems since the production rate of making depressions is increased because the cutting head cuts as the power unit moves forward. However, these automated systems for raising and lowering the cutting heads impose limitations above and beyond the cutting time required by the cutting head to complete its cut.
The maximum production rate of any cutting machine is limited by the amount of time required for the cutting head to complete each cut. Prior art systems, however, could not meet maximum production rates because of limitations imposed by the mechanical arrangements used to control the vertical motion of the grinding head. In addition, these mechanical arrangements are subject to excessive wear and maintenance.
Furthermore, the prior art cutting machines do not adequately self-align the cutting heads with the road surface, thereby requiring an operator to continuously monitor and manually adjust the cutting head as road surface changes, such as inclined surfaces, are encountered, in order to ensure the depressions are formed in accordance with specified dimensions.
Furthermore, it is often the case that the number of depressions in a given rumble strip and/or the size of the depressions in a given rumble strip are different depending on the job site. Accordingly, in order to accommodate these changes, the prior art systems require the replacement of the cutting head and/or a complete change of the mechanical control mechanism (eccentric wheel, cam/lever) in order to achieve the required depression sizing. Such reconfiguring of the cutting machine is time consuming and costly.